now if i download these updates and after when they are installed ....are ther some files to be deleted...like i am running mac OS X 10.6.6 so will it be deleted or overwritten....my main concern is will any additional space be used...thanks in advance..

Just download the Mac OS X.6.7 Combo Updater and it will handle everything. Any files that need deleting will be deleted automatically. Run Repair Permissions from Disk Utility before and after updating.

Hang on to those original install discs like grim death! Using OS X.7 or later make a bootable USB thumb drive before running Installer!

Just download the Mac OS X.6.7 Combo Updater and it will handle everything. Any files that need deleting will be deleted automatically. Run Repair Permissions from Disk Utility before and after updating.

What harryb said, but if Disk Utility shows any messages, don't get alarmed. This is perfectly normal (unless the message is printed in red -- if you see a message from Disk Utility in red, THAT you should pay attention to!).

In short, do the updates. They will take up a small amount of additional space (since they usually bring improvements), but they replace only the components they speak of and do not affect normal operations at all.